The use of foam in compressible printing blankets and other graphic art devices such as printing blankets, engraver's gums, box die mounting boards and drawsheets is well known in the art.
Compressible printing blankets offer printers an advantage over noncompressible printing blankets by eliminating the need for precise underpacking to achieve an acceptable amount of pressure between printing plate, printing blanket and a paper or other material to be printed. Foam is often used in these compressible printing blankets to keep the pressure relatively constant over a wide range of squeeze. The foams are normally present in very thin layers. It is important that the foam be of such a nature that it has good compression set resistance and uniform compressibility and uniform gauge (so as to print uniformly) and is capable of being applied (during the manufacture of the blanket) and cured to a uniform gauge.
Foaming agents and blowing agents i.e., compounds capable of releasing gases such as carbon dioxide by decomposition, normally at high temperatures, have been used to produce foams in the past from polymer latices and solutions of polymers in organic solvents. Such foams have been cured at high temperatures, over an extended period of time, using sulfur as a curative.
Such systems if used to produce foam layers where uniform compressibility, uniform gauge and good compression set resistance are important, could be deficient in that the high temperature operations of foaming, curing and water or solvent removal can result in nonuniform foam formation. This is particularly true where the operations are time consuming, and result in a partial collapse of the foam before sufficient curing has occurred to maintain the foam structure and gauge. Such deficiencies can contribute to nonuniform compressibility.
There is a need, therefore, for foams possessing good compression set resistance and uniform compressibility, which are capable of being formed and cured to uniform gauge.